289665-31-2Relevant academic research and scientific papers
How to predict activation barriers - Conformational transformations of compounds CH3C(CH2PPh2)(3-n)[CH2P(oTol)2](n)Mo(CO)3 (n = 1-3): Force field calculations versus NMR data
Beyreuther, Stefan,Frick, Axel,Hunger, Johannes,Huttner, Gottfried,Antelmann, Bj?rn,Schober, Peter,Soltek, Rainer
, p. 597 - 615 (2007/10/03)
Tripod metal entities tripodM are sterically congested systems. The conformations adopted by compounds CH3C(CH2PPh2)(3- n)[CH2P(oTol)2](n)Mo(CO)3 (n = 1: 1, n = 2: 2, n = 3: 3) will thus be largely determined by the repulsive forces acting in these molecules. The steric demand of the o-tolyl groups impedes their free rotation and enantiomerization processes referring to the compounds as a whole are sufficiently slow to permit their analysis by NMR techniques. Through a combination of line-shape analysis, EXSY methods, and coalescence experiments, the ΔG((+)) values for these conformational enantiomerization processes have been determined as ΔG((+))(298K) = 54.3, 57.9, 65.5 kJ·mol- 1 for compounds 1, 2, and 3, respectively. By an exhaustive search on a force field generated hypersurface, activation energies of 53, 57 and 69 kJ·mol-1 have been calculated. Thus, the force field approach correctly reproduces the dependence of the activation energy on the degree of o-tolyl substitution. Moreover, the force field simulation also gives an insight into the individual microsteps of the enantiomerization pathways.
